1. Field of the Invention
The present invention relates to combined read/write thin film magnetic heads used in floating-type magnetic heads and the like. In particular, the present invention relates to a combined read/write thin film magnetic head in which a flat layer is provided on a lower core layer in order to readily form a coil layer.
2. Description of the Related Art
A combined read/write thin film magnetic head shown in FIG. 7 includes a reading head having a magnetoresistive element 11 provided on a lower-shield layer 9 at a trailing side face 15b of a slider 15, and an inductive-type magnetic head h2 for writing deposited thereon. FIG. 6 is an enlarged cross-sectional view of the inductive-type magnetic head h2 and is taken along sectional line VI--VI of FIG. 7.
The inductive-type magnetic head h2 shown in FIG. 6 is provided with a lower-core layer 21 composed of a magnetic material having high permeability, such as a Fe--Ni alloy (permalloy). The lower-core layer 21 also acts as an upper-shield layer of the reading head having the magnetoresistive element 11. A gap layer (a nonmagnetic layer) 22 composed of aluminum oxide (Al.sub.2 O.sub.3) or the like is formed on the lower-core layer 21 and its circumference. An insulating layer (a resist layer) 23 composed of an organic insulating material is formed on the gap layer 22, and a coil layer 24 is spirally formed thereon as follows. A resist material is applied onto the insulating layer 23, exposed with a pattern for the coil layer, and developed, and the coil layer 24 is plated on the pattern using a low-resistivity material such as Au or Cu.
An insulating layer (a resist layer) 25 composed of an organic insulating material is formed on the coil layer 24, and an upper-core layer 26 composed of a magnetic material having high permeability, such as a Fe--Ni alloy (permalloy), is formed on the insulating layer 25. As shown in FIG. 7, the front end 26a of the upper-core layer 26 faces the lower-core layer 21 through the gap layer 22 having a magnetic gap G1, and the base end 26b of the upper-core layer 26 is magnetically connected to the lower-core layer 21. A protective film 27 composed of an insulating material, such as aluminum oxide, is formed on the upper-core layer 26.
As shown in FIG. 6, the length Lb of the region in which the lower-core layer 21 is formed is remarkably larger than the length La of the region in which the coil layer 24 is formed. The flat surface, formed on the lower-core layer 21, of the insulating layer 23 therefore has a length Lc sufficient to provide a flat region for forming the coil layer 24. As a result, the coil layer 24 is stably formed on the wide flat region above the lower-core layer 21 and defects of the coil layer 24 will be barely formed.
A recording current led to the coil layer 24 in the inductive-type magnetic head h2 induces a recording magnetic field in the lower-core layer 21 and the upper-core layer 26. Magnetic signals are recorded on a recording medium such as a hard disk by means of a leakage magnetic field between the lower-core layer 24 and the front end 26 of the upper-core layer 26 at the magnetic gap G1.
The total inductance of the inductive-type magnetic head h2 must be lower than a given critical value in order to achieve high density recording by means of high recording frequency. A decreased inductance can decrease the impedance and the time constant of the inductive-type magnetic head h2 in view of the circuit and improves high frequency recording characteristics. In the inductive-type magnetic head h2 shown in FIGS. 6 and 7, however, the lower-core layer 21 has a large inductance, because it has a large volume. A decrease in the total inductance in the inductive-type magnetic head h2 in response to high frequency recording therefore should be achieved by decreasing the inductance of the coil layer 24 by means of reduction of coil turns. The reduction of the coil turns, however, causes a decreased intensity of the recording magnetic field and is not capable of writing by a low electric power.
FIG. 8A is an enlarged cross-sectional view of a magnetic head, in which the length lb of the lower-core layer 21 is merely decreased and is smaller than the length la of the coil layer 24 for the purpose of the reduction of the inductance. In this case, the coil layer 24 is formed over a range larger than the lower-coil layer 24. It therefore is also formed just above bumps 21 at both ends of the lower-coil layer 24. Since the insulating layer 23 has slanted surfaces on the bumps 21, the coil layer 24 also has slanted surfaces above the bumps 21. In the step forming the coil layer 24, a resist material is applied onto the insulating layer 23 and a resist pattern 24a for the coil layer 24 is exposed through a mask. The exposed light is randomly scattered inside the resist material on the slanted surfaces of the insulating layer 23. As a result, the resist pattern 24a will have some defects 24a' on the slanted surfaces due to unsatisfactory patterning. Short-circuiting of the coil layer 24 based on the resist pattern 24a will therefore readily occur.
FIG. 9 is a cross-sectional view of an improved magnetic head, in which the lower-core layer 21 has a small length and the surface of the insulating layer 23 under the coil layer 24 is flat.
In the improvement, the region of the lower-core layer 21 is considerably smaller than the region of the coil layer 24, and a plating layer 28 composed of a nonmagnetic material such as copper is formed beside both sides of the lower-coil layer 21 so that these two layers have the same thickness. The gap layer 22 and the insulating layer 23 are formed thereon. Since the plating layer 28 having the same thickness as the lower-core layer 21 is formed beside both sides of the lower-core layer 21, the insulating layer has a flat surface and thus a coil having no defects can be readily formed.
In practical inductive-type magnetic heads h2, however, since the thicknesses of the gap layer 22 and the insulating layer 23 are small, short-circuiting will occur between the coil layer 24 and the conductive plating layer 28 due to defects, such as pin holes, in the gap layer 22 and the insulating layer 23. In inductive-type magnetic heads for high density recording, the thickness of the gap layer 22 which determines the gap length between the lower-core layer 21 and the upper-core layer 26 is too small to prevent short-circuiting due to layer defects.
Another type of magnetic head uses a nonmagnetic oxide, such as glass, SiO.sub.2 or Al.sub.2 O.sub.3, as the layer 28 at both ends of the lower-core layer 28 in FIG. 9, in which the nonmagnetic oxide layer 28 is formed on the substrate and the lower core layer 21, as shown in FIG. 10A, and the nonmagnetic oxide layer 28 formed on the lower-core layer 21 is removed by grinding to equalize of the level of the lower-core layer 21 and the level of the nonmagnetic oxide layer 28 as shown in FIG. 9. If the nonmagnetic oxide layer 28 is excessively ground, the lower-core layer 21 will be also ground and the magnetic characteristics of the lower-core layer 28 will deteriorate due to stress during grinding. If the nonmagnetic oxide layer 28 is left on the lower-magnetic layer 21, the head characteristics change due to the residual nonmagnetic oxide layer 28 under the gap layer 22, as shown in FIG. 10B.